Grid-controlled electron tube



April 15, 1952 A. H. MANKIN El'AL 2,593,044

GRID-CONTROLLED ELECTRON TUBES Original Filed April 5, 1946 X= DISTANCE INVENTORS ATTORNEY Patented Apr. 15, 1952 GRID-CONTROLLED ELECTRON TUBE Arthur H. Mankin, Chicago, Ill, and David E.

Sunstein, Cynwyd, Pa., assignors to Philco Corporation, Philadelphia, Pa., a corporation of Pennsylvania Original application April 5 1946, Serial No. 659,684. Divided and this application November 10, 1950, Serial No. 195,108

11 Claims. (01. 315-30) This invention relates to electron discharge tubes, and more especially to tubes of the gridcontrolled type.

A principal object of the invention is to provide an improved grid structure for electron disor windows is rendered more uniform.

Another object is to provide a grid structure which is so designed that the greater part of the electrons from an associated cathode, arrive at the grid plane all in substantially the same phase. As a result, it is possible to design tubes for very high frequency use wherein the tube functions by reason of the electron transit time between a cathode (either actual or virtual) and a succeeding foraminous grid.

A feature of the invention relates to an improved grid structure for electron tubes wherein each major grid opening or window is provided with special field-forming means for insuring that the potential gradient is substantially uniform throughout the plane of the window.

Another feature relates to a novel grid structure having spaced grid wires between which an electron stream is arranged to pass, each of said wires having supplementa1 and substantially co- 0 planar wires for controlling the potential fields in the plane of said grid wires.

A further feature relates to a grid structure for electron tubes having a plurality of spaced control wires, ordinarily referred to as grid laterals, which are arranged in groups, with the spacing between groups very much greater than the spacing between individual Wires of each group.

A further feature relates to a grid structure for electron tubes wherein each main grid lateral is provided with a pair of spaced auxiliary laterals. In accordance with this feature, the main laterals and the associated auxiliary laterals can be statically biased with relation to each other so that the potential field between the main laterals is rendered substantially uniform.

Another feature relates to an electron discharge tube having at least one grid, such for example as the signal control grid, constituted.

of grid laterals arranged in spaced groups of three or more per group. Each group has certain of its laterals biased or energized to a different extent from the remaining groups so as to maintain the potential field within the grid windows substantially uniform.

A still further feature relates to the novel organization, arrangement and relative interconnection of parts which cooperate to provide an improved grid-controlled electron tube.

Other features and advantages not specifically enumerated will be apparent after a consideration of the following detailed descriptions and the appended claims.

'In the drawing which illustrates certain preferred embodiments by way of an example:

Fig. 1 is a-generalized view of two conventional spaced grid laterals used in explaining the principles of the invention.

Fig. 2 is a composite structural and graph diagram to explain the usual potential field distribution with the conventional grid laterals.

Fig. 3 is a modification of the grid laterals according to the invention.

Fig. 4 is a composite structural and graph diagram to explain the functioning of a grid according to the invention.

Fig. 5 is a view, partly sectional, of a cathoderay tube embodying certain features of the invention.

Heretofore, in the design of grid-controlled electron tubes employing control grids of the conventional parallel grid wire type, it has been knownwhen a steady direct current potential is applied to or assumed by the grid, the potential distribution in the planar space between adjacent laterals is not uniform. We have found that this non-uniformity of inter-lateral potential gradient is the cause of certain drawbacks ingrid-controlled tubes. One of these drawbacks is the lower ratio of mutual transconductance 'to plate current that is obtained because of the rounded or gradual cutoff characteristic of ordinary grid structures, as distinguished from the ideal or sharp cutoif of the current tending to traverse the grid plans. These drawbacks become of increasing importance when the tube is used as a power amplifier or in the higher frequency circuits, particularly those wherein electron transit times between certain electrodes are ofimportance. However, in certain of its aspects, the invention is applicable to any grid-controlled tube where uniformity of potential in the plane of the rid is adesired characteristic.

Referring to Fig. 1, there is indicated a pair of spaced parallel wires b whose spacing is D and whose length is E. These wires may represent therefore a pair of spaced grid laterals such as are employed in any usual form of wire wound grid or planar grid. When such a grid is interposed in the path of an electron stream which for example is perpendicular to the plane of the laterals, and the grid is subjected to a direct current or other energizing potential which is different from the free potential existing in the plane of the grid due to the potentials on various electrodes adjacent to the grid (which potential the grid tends to assume when floating), the potential field between the conductors is far from uniform. Thus, as shown in Fig. 2, the potential of the space in the region between the wires b is represented by the curve H). The solid curve of Fig. 2 is the potential which obtains with grid wires of finite radius or thickness, whereas the dotted curve is that theoretically obtained with grid wires of zero radius or thickness. From this curve, it will .be seen that electrons arriving at the plane of the grid, will be subjected to difierent retarding or accelerating actions dependent upon the portion of the cathode from which they were emitted. In other words, considering the central region between the grid wires b (Fig. 1) arriving electrons will be subjected to a smaller retarding force, than the force acting on the electrons on either side of this central region. If the tube operates on the electron transit time principle, this inequality of actual interwire potential seriously limits the high frequency range at which the tube can be used, since the transit time for a given electron will be dependent upon the position of that electron within the grid aperture. Furthermore, this inequality militates against a very sharp plate current cutoff characteristic.

We have found that by supplementing the grid wires b with auxiliary or closely adjacent conductors in substantially the same plane, and by suitably energizing the wires in groups, it is possible to modify the interwire field characteristic so that it becomes substantially flat. One arrangement for accomplishing this is diagrammatically shown in Fig. 3, wherein each grid lateral may be considered as being tri-part and composed of three strands of wires 0., b, a. The wires 12 may be considered as auxiliary field controlling wires for the main grid laterals aa. Preferably, wires a are equally and closely spaced on opposite sides of the cooperating wire b, the spacing being suflicient to prevent short-circuiting when the wires are in the same plane. The wires 12 of all the sets may be connected to .a suitable negative biasing direct current source indicated as battery I I, while the wires 12 are, together, connected to a negative direct current biasing source I2 which may be lower in negative potential than the source I I. For example, if, in a conventional tube, the usual grid wires are biased negatively nine volts for linear operation, then, in the grid according to Fig. 3, wires b may be biased to more than -9 volts (e. g., -15 volts), while the wires (1 may be biased to substantially less than -9 volts (e. g., 1 volt).

With such an arrangement, the potential field in each grid window, is substantially uniform as indicated by the curve I3 (Fig. 4). The equation for the potential 1) at any given point in the region bounded by succeeding sets of the tri-part grid wires is approximately,

wherein in is the potential applied to wires b; w is the potential applied to wires a; D is the distance between the wires 1); h is the distance between wire b and the adjacent wire a; and the exponent n is the ratio of 122 to '01 (distances are measured between wire centers).

' It will be noted that, even though grid wires a may be positive, the presence of negative potential on wires 1) causes a deflecting field which tends to reduce the current drawn by wires a to an extent which may maintain the current drawn thereby substantially zero even though the wires or be several volts positive. Thus a screen grid built according to this coplanar array principle may be designed to draw no current, yet provide the desired accelerating and shielding function of an ordinary screen grid. In this application of the invention, the plate should be maintained more positive than the grid wires a, or other means should be provided to reduce secondary emission from the anode in order to maintain the screen current substantially zero.

It will be understood that the invention is not limited to any particular manner of mounting each set of three grid wires 0., b, a, nor to the use of exactly three wires, since the approximately flat field configuration may be obtained by arrays of 2, 3, 4, 5, or more wires in groups, each wire being suitably energized. In fact the more wires used in each group, the closer it is possible to obtain a perfectly flat field in the window between the groups.

While in the foregoing description, reference has been made to a grid structure wherein the grid wires are arranged in spaced groups of three wires per group, it will be understood that each group may consist of a greater number than three so as to render even more uniform the potential distribution between adjacent groups.

Fig. 5 shows the inventive concept embodied in a cathode-ray tube 35 of any well-known construction including for example the usual electron gun 36, and a beam deflector system 31 comprising one or more sets of deflecting elements. Suitably mounted between the electron gun 36 and the deflecting system 3'! is an annular electrode array comprising three concentric and substantially coplanar rings 39, to and M. The ring 39 corresponds functionally to the grid wires 12 in the embodiments of Figs. l-4, while the rings 40 and 4'! correspond respectively to the associated auxiliary grid wires a, a. The rings 49 and 4| are connected together and thence to a common lead-in conductor'42, as is the ring 39 with its individual lead-in conductor 43. The conductors 42 and 43 are connected respectively to suitable potentials as described above so that the potential field within the plane bounded by the ring 4| is substantially uniform.

While one particular embodiment of cathoderay tube has been described, itwill be understood that various changes and modifications may be made therein without departing from the spirit and scope of the invention.

This application is a division of application Serial No. 659,684, filed April 5, 19% and issued as U. S. Letters Patent No. 2,535,307 on December 26, 1950.

What is claimed is:

1. Electron tube apparatus, comprising, means to develop a beam of electrons, and means to subject said beam at a given plane to the action of a potential .field which is substantially uniform throughout, the last-mentioned means including a main ring-like electrode through which the beam is to pass, pairs of auxiliary ring-like electrodes substantially coplanar with the main electrode, one auxiliary electrode of each pair being of smaller diameter than the main electrode and the other auxiliary electrode of each pair being of greater diameter than the main electrode, leadin means for applying a predetermined bias to the main ring-like electrode, and other leadin means connected in parallel to the auxiliary electrodes to apply a difierent bias thereto for the. purpose of maintaining substantially uniform the potential field in the region bounded by the main electrode.

2. A beam control arrangement for electron beam tubes and the like, comprising, a main ringlike electrode, a first auxiliary ring-like electrode substantially coplanar with the main electrode and interiorly surrounding it in closely spaced relation, a second auxiliary ring-like electrode substantially coplanar with the main electrode and exteriorly surrounding it in closely spaced relation, a lead-in conductor connected to the main electrode for applying a predetermined bias thereto, and another lead-in conductor connected in parallel to the auxiliary electrodes to apply a different predetermined electrical bias thereto and to maintain a substantially uniform potential field within the boundary of the main electrode.

3. Electron tube apparatus, comprising, a gun for developing a beam of charged particles, a grid electrode system to be traversed by said beam and including a main grid ring, an inner auxiliary grid ring, an outer auxiliary grid ring, said grid rings being substantially coplanar and insulatingly spaced from each other to set up a substantially uniform potential field within the boundary of said inner ring.

4. Electron tube apparatus, comprising, means to develop a, focussed beam of electrons, a grid electrode system to be traversed by said beam, said system comprising a main grid ring, a pair of substantially coplanar auxiliary grid rings one spaced inside the main ring and the other spaced outside the main ring, a lead-in conductor connected to the main ring to apply one electrical bias thereto, and another lead-in connected to both said auxiliary rings to apply a difierent electrical bias thereto to maintain a substantially uniform potential field within the boundary of said inside ring.

5. A grid system for electron tubes and the like, comprising, a main grid ring defining an opening through which a stream of charged particles is to pass, and means to maintain the potential field in the plane of said opening substantially uniform throughout, the last-mentioned means including a first auxiliary grid ring spaced inside the main ring, a second auxiliary grid ring spaced outside the main ring, and means to connect respective biassing voltages to the main ring and to the auxiliary ring, all said rings being substantially coplanar.

6. A grid system according to claim 5, in which the radial spacing of the said rings is much 6 smaller than the radius of the main ring.

7. A cathode-ray tube having an electron gun to develop an electron beam, a grid system defining a grid window to be transversed by said beam, said grid system consisting of three closely spaced and substantially coplanar grid rings, the middle ring being provided with a lead-in for connection to a biassing source to bias it to a difierent direct current potential from that of the two remaining rings to maintain the potential field in said window substantially uniform throughout, said middle ring being of larger diameter than the first or inner ring to provide an annular space therebetween, and said middle ring being of smaller diameter than the third or outer ring to provide an annular space therebetween.

8. A cathode-ray tube according to claim 7, in which the auxiliary grid rings are biassed negatively with respect to the gun cathode to a different amount as compared with the negative bias of the main grid ring with respect to the gun cathode.

9. Electric signal apparatus, comprising, a cathode-ray tube having an electron gun to develop a beam of electrons, a beam-deflecting system, a screen, a grid system comprising a main grid ring defining a grid Window through which the beam is to pass, a pair of auxiliary grid rings spaced inside and outside of the main ring at a distance very much less than the diameter of the main grid ring all said rings being substantially coplanar, means to apply a predetermined electrical bias to the main grid ring, and means to apply a different electrical bias to the auxiliary grid rings for the purpose of maintaining an electric potential field in said window which is substantially uniform throughout.

10. A cathode-ray tube having means to develop a beam of electrons, a screen to be scanned by said beam, means located in the path of said beam and comprising at least two electrodes one of which surrounds the other in spaced and substantially coplanar relation to produce an electric field directed substantially parallel to the beam and whose intensity is substantially invariant in the direction transverse to the beam, and means to bias said members electrically in opposite senses to set up said transversely invariant electric field.

11. A cathode-ray tube according to claim 10. in which the said one of said electrodes more closely surrounding the beam is negatively biased with respect to the next surrounding electrode.

ARTHUR H. MANKIN. DAVID E. SUNS'I'EIN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,235,498 Herold Mar. 18, 1941 2,495,259 Jackson Jan. 24, 1950 2,519,172 Brown Apr. 15, 1950 2,535,307 Mankin et al. Dec. 26, 1950 

